Biomass as an energy source – that’s a phrase which everyone reading this post has read at least once in a life. For those who hasn’t, we can imagine biomass as everything living, doesn’t matter if it’s a cow or algae under the sea. By using it as an energy source we mean the various ways of conversion, some we’ve known throughout the centuries (like burning wood) some are more advanced and sophisticated. And that’s the topic of this post, well not entirely, because more than on the means (which I will also mention) I’m focusing on the product. The product is BIOHYDROGEN.
Biohydrogen as the name suggests is hydrogen gas made by renewable means which are mostly fermentation processes. There are also thermochemical ways of generating hydrogen but they are more energy demanding and we’re focusing on using waste as a feedstock. Waste, either domestic, industrial or wastewater from water treatment plants is considered a second generation biomass resource. The definition of second generation biofuels is following: ‘The resource base for the production of second-generation biofuel are non-edible lignocellulosic biomass resources (such as leaves, stem and husk) which do not compete with food resources.’  The other principle to turn biomass into H2 is based on biochemical processes. There are two main ways, which are only differentiated by the type of bacteria and by conditions they need to do their ‘work’. Those two are called dark fermentation and photofermentation. Like the names suggest those two processes need either sunlight or darkness. In both of those the bacteria consume various complicated carbohydrates and turns them into alcohols, acetone and small amounts of H2 and CO2 .
The dark fermentation is mainly anaerobic (conditions where no oxygen is present) process. The advantage of this process is as you think that it doesn’t rely on sunlight so it can work in day or night. The restrictions of this process are that the bacteria is highly dependent on the acidity of its surroundings and also on the fact that hydrogen pressure can’t build up too much as it lowers additional production .
If the dark fermentation bacteria are night owls then photofermentation bacteria are early birds, because only sunlight gives them energy to get up and work (quite literally!). Other then that they need some organic acids, some water and voilà there is H2 (also with some CO2 we can’t escape that really). The efficiency is better the with dark fermentation but there are a few drawbacks. The bacteria need a pre-treatment because the waste waters may contain toxic compounds also the need organic acids for them to work which can be a difficulty which we’re facing when utilizing this process 
Now when we’ve described main biochemical means of biohydrogen production there is an important question: Why all this? Can biohydrogen save us all from global warming, can it solve all our energy demand issues? Well, probably not. What hydrogen can offer that other fuels don’t and why should we care? It is undoubtedly a good question. For the most part it has highest energy density of any fuel! And when burned or used in fuel cells it only produces water vapour and no CO2 like other fuels . Also the worldwide demand for hydrogen was 73,9 Mt worldwide and about three quarters of it were made from natural gas and only small fraction of it was made renewable way according to IEA . The vital step to ensure sustainability is to move away from the utilization of fossil fuels even in this field and getting rid of our waste in doing so offer all the benefits. The main drawbacks are still it’s costs which can’t compete with generation of hydrogen the unsustainable way. If we look away from hydrogen that is currently mostly used in industry there are concepts of whole hydrogen ecosystem where the hydrogen is proposed to be used as energy carrier for electricity storage, because as we know the problem with renewable energy is mostly that we can’t efficiently store electrical energy for longer periods of time. Until long term storage technologies are developed our economies will still have to rely on fossil fuels and hydrogen could be the one that changes the path we’re currently on.
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